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In terms of the optionals(?), what's the difference between the two? I'm trying to pick up swift and it seems that the location of "?" matters and i'm having a hard time grasping the effect of having "?" in different places.

    var beaconGroup:GroupData = filteredArray.firstObject? as GroupData

    var beaconGroup:GroupData = filteredArray.firstObject as GroupData
shle2821
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  • possible duplicate of [What does an exclamation mark mean in the Swift language?](http://stackoverflow.com/questions/24018327/what-does-an-exclamation-mark-mean-in-the-swift-language) – Nikos M. Mar 11 '15 at 17:14
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    Actually there is no difference between both. The second is just a shorter form (syntactic sugar) of the first – qwerty_so Mar 11 '15 at 17:50

2 Answers2

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There is no difference between those two lines:

var beaconGroup:GroupData = filteredArray.firstObject? as GroupData

var beaconGroup:GroupData = filteredArray.firstObject as GroupData

In the first, the ? is unnecessary — firstObject already returns an Optional. Using the optional chaining operator without actually chaining a further member lookup or access expression has no effect.

In Swift 1.2 (currently available in the Xcode 6.3 beta), superfluous use of the optional chaining operator is a compile error:

error: optional chain has no effect, operation already produces 'AnyObject?'

rickster
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1

An optional in Swift is a variable that can hold either a value or no value. Optionals are written by appending a ? to the type:

var myOptionalString:String? = "Hello"

? are used in two normal ways:

1.Declare a optional var (just add ? after the type)

var strValue : String?

2.To judge var will respond to the methods or properties while being called

let hashValue = strValue?.hashValue

If strValue is nil, hashValue is nil. If strValue not nil, thus hashValue is the value of strValue.

Zigii Wong
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